In the past, electric forklifts, wheel chairs and golf carts have traditionally been powered by direct current (DC) motors. Typically, DC motors are longer than a similarly powered AC motor, because they require additional operational elements such as a brush commutator. The commutator provides a connection point between the current driving the motor and the moving parts of the motor. DC motor elements often require additional maintenance because of this connection of moving mechanical parts. For instance, brush and commutator wear require disassembly of the machine and replacement of these parts.
As in the diagram illustrated in FIG. 1, conventional electric DC motor 100 incorporates three-phase threaded terminal stud connections 105, which protrude through the non-drive end bell. These studs can be positioned at various angles to facilitate attachment of the drive cables. The M8 (8 mm) threaded termination studs 105 provide the primary external power connection point to the motor. Secondary DC electrical connections (e.g., brushes and commutator) are made internal to the motor 100. In the DC motor lead wire is used to electrically connect the brush assembly to the terminals. Lead wire consists of many fine strands of wire that are uninsulated from each other—there is only an outer jacket of insulation around all of the wires. Once this outer jacket is removed, the group of fine wires can be readily terminated to the terminal conductor thru brazing or other means.
In contrast, AC motors are mechanically simpler and have a shorter frame size because they lack the DC motor's commutators and brushes. AC motors typically have either permanent magnet or squirrel cage rotors and therefore only need to supply drive current to the stationary portion of the motor. In a conventional three phase AC motor design 200, shown in FIGS. 2A and 2B, lead wires 205 (lengths of wire connected to the individual AC phase coils) exit the center of the motor 200 at point 225 and are terminated at the center of the motor body. Each phase has a terminal mounted to an M8 threaded stud 210 molded to a Rynite terminal block 215. Simple corrugated tubing 220 is then used to cover each external phase 205 from the exit point 225 on the non-drive end bell to the terminal block 215.
There are several design and safety concerns with the conventional AC wire terminals illustrated in FIGS. 2A and 2B. As illustrated, lead wires 205 are covered in simple corrugated tubing 220 and exposed to the motor's external operating environment. The wires are not substantially insulated. People working around the motor are therefore exposed to a significant risk of electric shock. Moreover, in day-to-day operation this type of motor design is often mishandled by users that attempt to lift the motor by wires 205. The wires 205 are not designed to support the weight of the AC motor 200. This type of misuse increases the risk of live electric wires becoming unfastened from their terminals 210 and further increases the risk of electric shock. Also, the AC lead wires are bundles of magnet wires that exit the phase coils at 335U, 335V, and 335W (shown in FIG. 3E) respectively, each of the individual wires comprising the bundle have a minor layer of insulation on their exterior. The existence of the layer of insulation means that the bundle of wires cannot be readily terminated to the terminal conductor. This is due to the high temperatures required to vaporize off the layer of insulation which eliminates brazing and the contaminating effect of the vaporized insulation layer to the resulting bundle strength which makes electrical resistance fusing or welding a problem. Removal of the insulation layer on each individual wire is possible but time consuming.
One conventional solution involves a two step process: (1) placing a ring of conductive material, such as a conductive ferrule, around the bundle of magnet wire with the insulation still in place and electric resistance fusing the wire bundle and the ferrule together; and (2) connecting the ferrule to the terminal conductor by brazing, soldering or other means to provide an electrical connection.
Also, as illustrated in FIG. 2A, the power connection location is fixed at the center of the conventional AC motor. Typically, end users prefer power connection points that can be positioned at various angles around the exterior of the motor to accommodate varied cable lengths similar to the DC motor design.